Where Did UNIX Come from and why Are There Different Versions of UNIX?

The first efforts at developing a multi-user, multi-tasking operating system were begun in the 1960's in a development project
called MULTICS. While working for Bell Telephone Laboratories in 1969 and 1970, Ken Thompson and Dennis Ritchie
began to develop their own single-user, multi-tasking small operating system and they chose the name UNIX. Their initial goal
was simply to operate their DEC PDP machines more effectively.…